Method of forming propeller hubs



Oct. 5, 1948. (5. w. HARDY 2,450,660

METHOD OF FORMING PROPELLER HUBS Filed Nov. 15, 1945 2 Sheets-Sheet 1agoyzw ATT'O/QA/EV.

Oct. 5, 1948. e. w. HARDY 2,450,660

METHOD OF FORMING PROPELLER HUBS File'd Nov. 15, 1945 J 2 Sheets-Sheet 2AW/IEN-T OR I 60900 /Al os Patented Oct. 5, 1948 UNITED STATES aTaN TEMETHOD OF 'FQRMING PROPELLER HUBS Gordon W. Hardy, Euclid, Ohio,assignor to The Marquette Metal Eroducts Company, Cleveland, Ohio, acorporation of Ohio Application November 15, 1945, Serial No. 628,771 6Claim-s. (Cl. 29 -156.8

This invention relates to a method of making hubs for aircraftpropellers, and more especially to making such hubs large enough tocontain blade pitch controlling and equalizing mechanism for changingpitch during flight. The above indicates the general object.

A further object is to provide a method of forming a propeller hubarranged to support three blades and in such manner that the externalexposed surfaces are smooth, gradually merging into each other tominimize noise and drag and Without requiring timetaking hand finishingoperations such as heretofore considered unavoidably necessary inpropellers of that type or class.

Another object is to provide a simple and efficient method of makingahub comprising a central portion in th form of a spherical zone andequidistantly spaced radiating arms in a plane cutting an axial orabsolute center of said zone.

Other objects will become apparent from the description below of themethod as applied to one'exemplary form of propeller hub (three bladescontrollable pitch).

" In the drawings, Fig. l is a plan or end view of a hub blank in theform of a rough forging after two series of operations have beenperformed on it, namely, central boring and radial center socketforming; Fig. 2 is a side elevation or edge view of the forging in thesamecondition (partly in radial plane section as indicated on Fig. 1)Fig. 3 is an end View corresponding to Fig. 1, showing further progressof the work of forming a propeller hub from the forging; Fig. 4 isad'etail sectiona'kl View illustrating one type of 'g-age used totestwall thickness after rough formation of "spherical inner and outersurfaces of the hub; 5' is an end View of the semi-finished hubfollowing the operation depicted by Fig. 3 and mounted for drilling andcounterboring blade receiving armportions of the hub; Fig. 6 is a viewof the still partially finished hub as mounted for recuttihg (turningand facing) central hub flange surfaces after hardening; Fig. '7 a sideview of another form-of gage andgin section, acenter ings'ocket'edportion of the hub to which the gag is applied; Fig, 3 is a View similarto Fig. 6 showthe nearly finished hub as mounted for cut ting or truingcertain centering sockets to precision form as reference and. centerpositioning surfaces; Fig. 9 is a view ofthe hub as mounted for internalgrinding of the blade supporting arms or barrels of the hub; Fig. 10is asimilar View showing the manner of externally grinding and/or polishingthe rincipalexternal spherical central bodyand cylindrical barrelsurfaces of the hub; and Fig. 11 is a detail sectional View showing onemanner of plugging the centering socket openings in the hub wall priorto installing the hub in a propeller assembly.

The term spherical as used herein means hav ing characteristics of asphere or part of a sphere. Referring to the drawings Figs. 1 and 2, theblank I there shown (partly Worked upon) will be described, by Way ofexample, as a steel forging' in the form of a flat block, the edges ofwhich define roughly, as indicated in broken lines 211, an irregularhexagon with alternately equal sides but preferably the blank is forgedmore nearly to the shape of the finished hub as illustrated in fulllines at 2. The forging may have a generally triangular or spherical-1yrounded central portion 3 and radial arms 4 spaced apart about thecenter of the forging. The forging, in any event, has arm port-ionscorresponding in position to the arms 4 somewhat longer or furtherradially ex tended than. the blade supporting arms or barrels of thefinished hub (see ,Fig. 1-0) and the central portion of the block is ofa thickness which is somewhat greater than the axiallength of the hub tobefor med. The forging is preferably electric-furnace-producedunkilledsteel on the gen eral order of 3140- ,Nichrome steel as identified, forexample, in an American Steel 8: Wire Company bulletin published January1935, asOf-- ficial S; A. E. Standard Steel Specifications. Any othersteel which may be heat treated and surface hardened to something lessthan 50 Rockwell without appreciable distortion in fairly large hollowpieces with relatively thin walls may be used.

The blank or forging l is first centrally bored.- as by supporting theblank between self centering chuck jaws (e. g. three interconnectedjaws) of a machine tool on the order of a lathe or boring mill. The jawsof the chuck may be forced against the outer ends of the arms or againstsymmetrically disposed surfaces between the arms. In any operations inaccordance herewith requiring such mounting in a chuck, the work pieceis usually forced against the main chuck face to bring the, arms into (acommon plane perpendicular to the chuck axis before the jaws are set. Thboring to form the central generally spherical cavity indicated at 5 anddefined in' part by inturned circular fl'angesfi and 1 maybe done on aHall planetary machine. The flanges 6 and i would, in that event, be atleast partially turned on thesame machine; One main central outsideface" of the forging as at F, Fig .3, is finished in the same machine onand around one flange 6 or I substantially to finished position forreference purposes. The spherical cut at 5 is a final cut and is madesubstantially smooth, being generated as a true sphere about the pointA, Figs. 1 and 2, as the center and located with reference to the firstfaced surface F mentioned. One important boring operation partlyillustrated by Figs. 1 and 2 is to finish form the inner peripheralsurfaces 8 and 9 of the flanges 6 and l which, in cooperation with theend face F, become reference surfaces upon which subsequent operationsare based.

The forging is now placed on a dividing head (not shown) as of a millingmachine, using the surfaces F, 8, and 9 to locate the piece and with atravellingdrilling fixture, with the drill chuck axis midway of the topand bottom of the forging, in position for drilling parallel to theplanes of the flanges 6 and l. The centering drill or drills on suchdrilling fixture forms or form three coacting pairs of centering socketsin the forging, the elements of which pairs lie on coplanar axesconverging at the center A and spaced exactly 120 apart. The threecentering sockets ID are through holes intersecting the innerspherically bored surface 5. Those holes are precision counterbored asat 12, Fig. 1, to uniform depths successively about the forging whilemounted on the dividing head and turned thereon to three of the socketforming positions. When forming the conical surfaces defining thecounterbores l2, the active movement of the drilling fixture at eachoperation is limited by a suitable single stop so that the conicalshoulders on the circles defining the inner ends of the counterbores l2(see Fig. 4) are exactly the same distance from the axis of the hub. Thedepths of the centering counterboring at H are similarly controlled andlimited. The axes of all the centering sockets are located in a commonplane and, in the exemplary construction illustrated, are substantiallyexactly halfway between the inner faces of the two inturned flanges 6and l, which is also the position of the center A of the sphericalboring 5. The position along the axis of the central bore or cavity forthe centering drilling may readily be determined by using said face F asa reference plane. Scribe marks such as shown at l4 in Fig. 2 are nowmade on the blank parallel to the axis of the centerborlng 5 andintersecting the axis of each centering socket NJ to define the limitsof subsequent external spherical turning operations as will be describedbelow.

For turning the external spherical surfaces (one at Sat, Fig. 3) and theblade supporting barrelforming arms at Go, the blank is mounted in alathe and located successively by the diametrally disposed pairs ofcentering sockets l and H. Onethird parts only of the spherical surfaceportions 3a are rough and finish turned for each -mounting of the blankin the lathe. The arms 4 may each be fully turned externally nearly todesired final shape (somewhat oversize). The spherical rough and finishsurface turning is terminated at the scribe marks l4.

As each two adjacent sphere surface portions 311 of the blank arefinished turned to the associated scribe marks M, the thickness of thewalls of the hub adjacent the centering sockets l0 may be checked with aflush pin gauge of the character shown at H5 in Fig. 4. The flatshoulder l6 of the flush pin gauge rests on the spherically turnedsurface and when the inner end I! of the plug of the gauge is found, asby finger test, to be flush with the inner spherically bored surface 5,the spherical turning passes inspection. The spherical form to which thecentral portion of the hub is turned is left oversize suficiently toprovide for removal of a small amount of stock later by grinding and tocompensate for expected slight change in shape during heat treatment.

The hub blank, Fig. 5, is now mounted on a dividing head as in the caseof forming the centering sockets l9 and l l (e. g. on the same mandrelas previously used or a similar one), and the three blade mountingbarrel-forming arms are rough drilled as at 26 along the axes of thecentering sockets H. The drillings 20 intersect the spherically boredcentral hub cavity surface 5. Then suitable enlargements of the cavitiesand seats (not shown) for blade mounting bearing assemblies etc. areformed by counterborings of suitable type depending upon the nature ofthe blade mounting desired. 2! shows a typical rough boring tool.Threads may be formed in the barrels to receive blade locking nuts aswell known in the art after drilling and boring of the arms 4 and whilethe piece is mounted as just described.

The nearly finished hub 49, when completed by successive operations on adivided head as described in connection with Fig. 5 and with allnecessary bolt, dowel, etc. holes (not shown) completely formed, is thenheat treated to harden all external surfaces to such extent that theywill adequately resist accidental disfiguration in use and, in respectto the internal surfaces of the barrels, to such extent that any ofthose surfaces can be made to serve directly as bearing races (withoutrequiring bearings race sleeves). Hardening to between 42 and 4'7Rockwell is adequate and does not prevent formation of further cutting(truing) operations as by turning with carballoy tool points. Hardeningof steel of the class earlier referred to herein increases the tensilestrength as much as 8%, which insures that the spherical walls of hubwill not change in shape under test and severe loading stress, and thatthe blade mounting barrels will not become elongated or otherwisedistorted by the enormous forces imposed upon them in supportinpropeller blades duringhigh speed rotation in flight. Movement of themetal during hardening is usually insignificant.

The hardened, practically finished hub 40 is now mounted as in a threejaw chuck as indicated at 25, Fig. 6, and the inner peripheral surfacesof the flanges 5 and "l and the front and rear surfaces thereof arefinish bored and faced by use of appropriately shaped cutting tools. Theouter face of the flange (6 or 1) which is to serve as the rear flangein the propeller is finished first in order that it can later be used asa reference surface in forming the forward face of the forward flange onwhich a blade pitch adjusting servo motor block (not shown) may becarried.

To mount the hub on the chuck in forming both flanges 6 and l, the hubmay be placed with the three jaws 25 lightly engaging the spherical partof the hub between the barrels 44 or the ends of the barrels; a presserplate (not shown) is disposed across the hub flange nearest the tailstock, and the tail stock is forced against the plate to press theflange nearest the head stock firmly against the chuck plate or head todispose the axes of the barrels ea in a common plane of rotation on thechuck. The chuck jaws are then tightened against the hub. Then theboring and facing operations are performed on the hub by appropriatetools.

The hub (Fig. 8) is now placed on a dividing head supported centrally aswhen first forming one the center sockets, and the counterbores' 112ofthe-sockets lo' between the barrels 44' are precision cut to finalform. This removes any misplacement of the centering sockets which mayhave occurred during hardening. Si in Fig. 8 represents a suitable toolwith carball-oy cutting teeth or points such as may be used to finalfinish the counterbore surfaces T2 of the centering sockets -l"9'.Incidentally, the through. drilling- .of tlicso'ckets is into theinner-cavity surface :5 may be doneby the carballoy tool whilethesockets, since the throughholescf. the sockets have not had to serve anyessential purpose:thus far. A flush pin gauge of the type: shown by Fig.rat 2'? having precision related reeler plug and conical socket engagingsurfaces- 28 and 28 re spectivel y is now used to check the-trucdcentersockets to with reference to the inside spherical. boring surface 5. Theplug o-ithe flush pin gauge passed into the through openings of thesockets l d-are felt-by a finger to Toe-flush with the cavity surface 5to make the tests. Since the centering socket counterbores as true'd bythe tool :H are: identical distances from the center of the and the wallthickness as measured bycach flush pingau'g'ing operation is the sameateaoh centeriirg socket, the central portion of the hub is necessarilybalanced for rotation and the inside and outside spherical surfacesareknown to be concentric. The hub is now ready to receive final finishgrinding internally of thebarrels-il l.

The centering socket trulng operations c'oun t'erbores i2) provideprecision reference surfacesby', which positioning shoulders for theblade mounts (bearing, sleeves-, etc.) may be finish ground or otherwiseprecision finished, so that blades of equal weights at correspondingradially spaced points and pressed against the shoulders will be certaintobalance aboutthe center of retation of the hub.

Referring 'to- Fig. 9-, the hub 40 is placed in a four jaw chuck oz,such as of a lathe headstock with two of the jaws 33' (one shown)"gripping the forward and rearward main --central faces of the hub at theflanges" 6- and 1', and the other two jaws 3E gripping the outer ends ofthe barrels or in positions Md. The arm or-bctrrelat position R tz/' 1sthus presented centrally ofthechu-ck axis where-it may be centered bythe-headstock center point 35, left Fig.9, engaging a centering socketIII in Cooperation with a V-s-l'rape'd work lest 36 fixed on the machinetool bed and having any suitable-friction reducing-means 'ior con tactwith the associated barrel at My (rollers-or soft-metal strips notshown). The inner peripheral. surfaces of the barrels i4 arenowfinishgr'oundsucessiva ly,-one;barrel at each mounting of the-hub inthe chuck, by a suitable self contained grinder unit (not shown-)-slidably mounted onthe machine toolbed for movement parallel to and/orlaterally of the chuck axis as well understood in the machine tool art.

Referring to Fig. l0,-thehub is now mounted in a four" jaw chuck or thesame-chuck as described in relation to Fig. 9 with the headstock: centerpoint 35 engaging one of the sockets N (at the trued counterbore surfaceI2) andthe tail stock center point engaging a centering socketin aturned mandrel or dummy plug 3% nicelyfittlng the'i'nner finishedsurface of the barrel which is-align'ed with such socket- Ill. Somounted suceessrvely-in three positions, allexternal, sphericalandcylindrical surfaces are final ground accurately to size and allexterio surface-distortions due-to heattreatmentardrcmoved;

' as illustrated by Fig ll.

In Fig. .10; 45 illustrates a; portion. a profile grinding wheel set upfor traversing movement only at right angles tolathe axis so thatthe:one third part so of the spherical suriace, the cylindrical externalbarrel surface 4 8,. and. both: radius surfaces 49 50 are ground, in oneor more operations per mounting depending upon the particular wheelprofile or profiles used, as the hub is turned slowly by the lathe".Preferably surfaces 3b, 48,. so and 50 are all doncwith. one grindingwheel to save time. Due to the fact that the counterbores of thecentering sockets ill have all been determined to be identicallypositioned with reference to the :hubccnter, spherical profile grindingoperation, if carried out to the same point with reference to respectiveblade barrel axes on each above describedv mounting of the hub, therecan be no possibilityrof error in forming the defining sphericalsurfaces of the central part of the hub, assumingof course that thewheel. used has proper profile as easily be provided; that the wheel isnot moved axially between successive operations, and that' the previousoperations performed on the hub have leftv sufficient metal for removal.by final grinding.

The final finish grinding. operations on thebarrel flanges orthickenedportions 151 of the hub are preferably affected by aseparategrinding wheel (not shown) either before or after profile grinding asabove described, but while theshub is mounted as in Fig; .10. Absolutelyno hand finishing operation is necessary .on any part of-the exteriorhub surface.

The finished hub .shownsby 10 ready for use in a propeller such asshotvnby any of my prior applications, Serial No.v 4516,398 filed: February19, 1 948; Serial/No. 498,492 :filed August: .13, 1943, issued as PatentNo. ,433',90, January :6, 1948; or Serial.v No. 528,412. .file'd. March528,. 1944-. The particular design shown (except for details purposelyomitted from the illustrations submitted herewith) is forthecontrollahlepitchproe peller substantially as shown in the last abovementioned application. As there shown, one imturned flange 6 or ".1hereof when provided "with suitable bolt onstud receiving holes.) suports a hub carrier which fits the engine crank shaft and the other hasa hydraulic servo motor unit and spinner secured thereto. The servomotor, through appropriate blade pitch changing and equalizinggearinglocated in thecentral space of the hub defined by the surface 5and the flanges, adjusts the blades .whichsare swivelled. the barrelscorresponding to those at M hereof.

Before installing the hub in the: propeller assembly, -al1 the centerlngso'ckets to areyp-lugged The plugs, as shown, are in the form of rivets"52 having. heads-filling the countersunk portionsfl' of the sockets andshanks filling the through holes which intersect the inner surface 5.The shanks are riveted over at :5! on the inside of the hub.

While the spherical portion of the hub as shown, neglecting the barrelforming arms, is ,a

bisymmetrical or central spherical zone, it may be any other sphericalzone or a sphere with one segment only removed. In that case, the closedregion of'the sphere would constitute the spinner adapted to support.blades,..the procedurecom 7-,, prising boring a circular cavitycentrally through a metal blank having three equally spaced radial armsso that the arm portions of the blank radiate from the center of thecavity, supporting the blank at periphera1 portions of the cavity forrotation on a fixed axis about the cavity center and, while sosupported, forming centering sockets axially of each of the arms of theblank and additional centering sockets in intermediate portions of theblank angularly equidistant from the arm socket axes, and then usingsaid sockets in pairs aligned diametrally of the cavity to locate theblank successively into three positions and, while so located in saidpositions, cutting the arm portions of the blank into generallycylindrical form and the arm-connecting portion of the blank intogenerally spherical form.

2. In a method of forming a propeller hub for a three-bladed propeller,the procedure comprising starting with a blank having a central bodyportion and three coplanar arms radiating therefrom 120 apart, boringthe central body portion in a manner to form a circular cavity open atleast at one side of the blank and whose axis extends at right angles tothe common plane of the arms, mounting the blank for rotation usingperipheral portions of the blank adjacent the cavity for engagement withan indexable support and, while so mounted, forming centering sockets120 apart about the cavity center in the outer ends of the arms and anadditional set of centering sockets 120 apart, 60 from the axes of thefirst mentioned sockets and in the wall of the body portion defined inpart by the cavity, rotarily mounting the blank by using diametrallyopposed pairs of sockets, one from each set, to locate the blank and,while so mounted and turned, cutting the arms into generally cylindricalform and portions of the central body portion into generally spheri calform wherever contiguous to the generally cylindrical surfaces.

3. In forming. a three-bladed propeller hub from a metal blank having acentral portion and radiating arms 120 apart, the method comprisinggripping the blank and boring a circular cavity through the centralportion transverse to the plane of the arms, using a marginal portion ofthe cavity for centering contact with an indexable support for rotationof the blank into positions enabling formation of coacting pairs ofcentering sockets in the blank axially of the arms, one at each arm endand the others axially opposite the arms and between adjacent arms, thensupporting the blank successively for rotation about the axes of thearms on said centering sockets whereby to turn the arms into generallycylindrical form and the central portion of the blank intogenerallyspherical form contiguous to said cylindrical surfaces, then, whileusing said marginal portion of the central circular cavity forengagement with an indexable rotary support, axially boring the armsfrom their outer ends to form blade supporting sockets, heat treatingthe hub thus nearly completely formed to harden the surface portions,mounting the hub for rotation in the plane of the arms about thecavity'center and truing peripheral and end face portions of the hubadjacent the central hub cavity to final form, then mounting the blankwith the truecl peripheral surface engaging an indexable support andrefacing the centering sockets which lie between the arms to identicaldistances from the hub center, mounting the hub by gripping the same atfour points successively to finish the inner surfaces of the bladesupporting sockets identically in reference to th refaced centeringsockets, and finally rotarily mounting the hub using the finished bladesupporting sockets successively in cooperation with the respectivelyopposite refaced centering sockets to finish or polish the exteriorspherical surface portions of the hub and adjacent external cylindricalportions of the arms.

4. In forming a. three-bladed propeller hub from a metal blank having acentral portion and radiating arms apart, the method comprising grippingthe blank and boring a circular cavity through the central portiontransverse to the plane of the arms, using marginal portions of thecavity for centering contact with an indexable support for rotation ofthe blank into positions enabling formation of coacting pairs ofcentering sockets in the blank axially of the arms, one at each arm endand the others axially opposite the arms and between adjacent arms, thensupporting the blank successively for rotation about the axes of thearms on said centering sockets whereby to turn the arms into generallycylindrical form and the central portion of the blank into generallyspherical form contiguous to said cylindrical surfaces, then, whileusing said marginal portions of the central circular cavity forengagement with a rotary support, axially boring the arms from theirouter ends to form blade supporting sockets, heat treating the hub thusnearly completely formed to harden the surface portions, mounting thehub for rotation in the plane of the arms about the cavity center andcutting inner peripheral portions of the hub adjacent the central hubcavity to final form, then mounting the blank with said inner peripheralsurface engaging an indexable support and re-forming the centeringsockets which lie between the arms to identical distances from the hubcenter, flush pin gaging the reformed surfaces of the centering socketswith reference to the central cavity inner wall, mounting the hubsuccessively for rotation on axes of the arms and re-formed sockets tofinish the inner surfaces of the blade supporting sockets identically inreference to the re-formed centering sockets, and finally rotarilymounting the hub using the finished blade supporting socketssuccessively in cooperation with the respectively opposite re-formedcentering sockets to finish the exterior cylindrical and sphericalsurface portions of the hub.

5. In forming a three-bladed propeller hub from a fiat three-armedblank, the method comprising gripping the blank as in a conventionalchuck and turning a circular spherical cavity through the center portionof the blank, using inner limiting circular surfaces adjacent the cavityfor centering contact with an indexable support for rotation of theblank and then forming coacting pairs of centering sockets in the blankaxially of the arms of the blank so that one element of each pair ofsockets lies between adjacent arms and the other element is on one ofthe arms, then supporting the blank successively for rotation about theaxes of the arms on said centering sockets whereby to turn the arms intogenerally cylindrical form and the entire central portion of the blankinto generally spherical form contiguous to said cylindrical surfaces,then, using the inner limiting circular surfaces adjacent the cavity forrotary support positioning of the blank and axially boring the arms fromtheir outer ends to form blade supporting sockets, heat treating the hubthus formed to harden the surface portions, mounting the hub forrotation in the plane of the arms about the cavity center and refacingperipheral portions of the first formed circular limiting surfaces, thenmounting the blank with the refaced surfaces engaging an indexablesupport and truing the centering sockets which lie between said arms toexact identical distances from the hub center, mounting the hub forrotation about the axes of the arms successively to finish the innersurfaces of the blade supporting sockets identically in reference to thetrued centering sockets, and finally rotarily mounting the hub using thefinished blade supporting sockets successively in cooperation withrespectively opposite trued centering sockets to finish grind theexterior aircular, cylindrical and spherical surface portions of thehub.

6. In a method of forming a propeller hub adapted to support threeblades, the procedure comprises starting with a generally flat forgedsteel blank with three equally spaced arm portions and a connectingcentral body portion, boring a generally spherical cavity in the centralportion and centrally of the blank so that the spherical limits of thecavity terminate between the side- Walls of the blank, and additionallythrough-boring and turning the blank around the spherical cavity and oneach side of the blank to form inturned concentric flanges for mountingthe finished hub, mounting the blank on a rotary support, centeringlyengaging the inner limits of the flanges and, while so mounted, formingsix equally angularly spaced centering sock- 10 ets all of which arecoaxial with the arm portions and which are diametrally aligned in pairsacross the center point of the spherical cavity, three of the centeringsockets entering the cavity at spherical surface portions thereof,mounting the blank successively in three positions for rotation aboutcoacting pairs of centering sockets and, in each position, turning oneof the arm portions of the blank generally cylindrically and an adjacentone third portion of the connecting portion spherically, axially boringthe arms at their outer ends to receive the blades, heat treating thehub thus formed to harden it, reforming and fiush-pin-gaging thecentering sockets which intercept the outer spherical surface withreference to the spherical surface of the cavity, and finally surfacefinishing the spherical and cylindrical external surfaces while usingthe centering sockets and the blade receiving bores of the arms forrotarily supporting the hub.

GORDON W. HARDY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 420,338 Everson Jan. 28, 18901,616,150 Teller May 2, 1923 1,915,657 Findlater June 27, 1933 2,285,772Groene June 9, 1942 2,344,242 Flygare Mar. 14, 1944 2,369,828 HumphreysFeb. 20, 1945

